Add agent/flow meta information to AI Catalog show page

• Add new component ai_catalog_item_meta.vue (we can consider creating different components for agent/flow; naming can change if you can think of something better).
• Add About section with "created_at", "updated_at" values. (who created, updated, made it public, etc. will be visible through Audit Events -- #566901)
• Could add "Made by GitLab" (this is available)

Designs and prototype available in #568950

Icons available here: https://gitlab-org.gitlab.io/gitlab-svgs/